Former presidential candidate Mitt Romney and former heavyweight boxing champion Evander Holyfield stare each other down at the weigh-in ahead of their upcoming charity boxing match in Utah on Friday night. REUTERS/Jim Urquhart.

Republicans are seeking to erode a geographic polarization that has grown more pronounced in recent decades as Americans have gradually sorted themselves into ideologically uniform neighborhoods, with Democrats clustering in densely populated cities and suburbs and Republicans scattering to distant exurbs and rural areas.

Possible Republican presidential candidate and New Jersey Governor Chris Christie greets supporters after speaking at the University of New Hampshire at Manchester, in Manchester, New Hampshire, May 12, 2015. REUTERS/Dominick Reuter